1. Field of the Invention
The present invention relates to a calibration method for a lithographic apparatus and to a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (resist). Instead of a mask, the patterning means may comprise an array of individually controllable elements that generate the circuit pattern on an impinging light beam.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one pass, and scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
A significant problem in a lithographic apparatus using an array of individually controllable elements is uploading the data necessary to set the pixels of the array of individually controllable elements. To achieve throughputs and resolutions comparable with mask-based lithographic apparatus, maskless systems typically use data transfer rates of 80 terabits per second, or more. A typical array of individually controllable elements may have pixels of about 8 μm×8 μm with an array of pixels of about 1000×4000 pixels. Multiple communication lines need to be operated in parallel to achieve the data rates desired. Switching rates will be high, and thus there is a large heat dissipation in a small device. Also, the necessary addressing circuitry is complex and difficult to fit in a small space.
For example, U.S. Pat. No. 6,388,798 B2 (“the '798 patent”), which is incorporated by reference herein in its entirety, discloses a system using a spatial light modulator, specifically a liquid crystal light valve (LCLV), on one side of a substrate and a microprocessor on the other side of the substrate. Electrical connections between the microprocessor and spatial light modulator are made by metal-lined vias extending through the substrate. The resulting structure is shown in FIG. 4 of the '798 patent. The vias are connected on the microprocessor side of the support to the metal one metallization layer (M-one) and the microprocessor is built on top of that. Bumps are used to connect the microprocessor to a PCB.
The spatial light modulator disclosed in the '798 patent is intended for use in portable or handheld devices and home entertainment apparatus. The integration of the microprocessor on the same substrate makes the device more compact, which is its principal advantage, and also enables ancillary optics in home entertainment devices to be made smaller as well. The '798 patent does not consider arrangements for addressing the pixels of the spatial light modulator, and proposes no means of improving data transfer rates.
Therefore, what is needed is a spatial light modulator suitable for use in a lithographic projection apparatus that is able to be programmed at high data transfer rates.